Investigating microbleeds and white matter hyperintensities in TBI at a tract-level: A DTI study.

OBJECTIVES

This study aimed to determine whether focal MRI lesions such as microbleeds (MBs) and focal white matter hyperintensities (FWMHs) serve as reliable and specific markers for tract-level white matter injury in traumatic brain injury (TBI).

MATERIALS &

METHODS

Twenty-two patients with moderate-to-severe TBI and 22 age-matched healthy controls underwent MRI on a 3 T Siemens Prisma scanner. Imaging included susceptibility-weighted imaging (SWI), fluid-attenuated inversion recovery (FLAIR), and diffusion tensor imaging (DTI). Focal lesions were manually identified on SWI and FLAIR and mapped onto tractography reconstructions. Diffusion metrics-fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were compared between lesion-affected tracts, contralateral normal-appearing white matter (NAWM), and corresponding control tracts. Statistical analyses were performed using repeated measures ANOVA with Greenhouse-Geisser correction and Bonferroni-adjusted post hoc tests for FA. Friedman tests were conducted for MD, AD, and RD, followed by Bonferroni-corrected Wilcoxon post hoc comparisons.

RESULTS

In this study, we identified 27 MBs and 66 FWMHs intersecting white matter tracts. We observed notable differences in diffusion metrics when comparing lesion-affected tracts to healthy controls. In MB-affected tracts, fractional anisotropy (FA) differed significantly (p = 0.002), while mean diffusivity (MD) also showed a significant alteration (p = 0.002), along with radial diffusivity (RD) (p < 0.001). Similarly, in FWMH-affected tracts, significant differences were observed in FA (p < 0.001), MD (p < 0.001), axial diffusivity (AD) (p < 0.001), and RD (p < 0.001). However, we did not find any significant differences between lesion-affected tracts and the contralateral normal-appearing white matter (NAWM).

CONCLUSION

MBs and FWMHs do not co-localize with axonal injury at the tract level but indicate a global white matter damage.